Conformance with ISO 13485

21 CFR 820 is the current quality system for medical devices used by the FDA. There is no requirement of conformance with the ISO 13485. Each standard (21 CRF 820 and ISO 13485:2016) may have additional requirements, but the requirements do not conflict with one another. While 21 CFR 820 compliance is required by law for the commercialization of medical devices in the United States, ISO 13485 is voluntary. 

If you need information on the Differences and similarities between FDA 21 CFR Part 820 and ISO 13485. please read article on the following link: 

https://advisera.com/13485academy/blog/2017/10/05/differences-and-similarities-between-fda-21-cfr-part-820-and-iso-13485/